Electrolytic cells



United States Patent 3,527,688 ELECTROLYTIC CELLS Umberto Giacopelli,Rosiguano-Solvay, Italy, assignor to Solvay & Cie, Brussels, Belgium, acorporation of Belgium Filed Dec. 28, 1966, Ser. No. 605,247 Claimspriority, application Belgium, Dec. 29, 1965, 22,216, Patent 674,452Int. Cl. Btllk 2/08, 3/00, 3/04 US. Cl. 204-242 3 Claims ABSTRACT OF THEDISCLOSURE The anodes of electrolytic cells, particularly diaphragmcells for the electrolysis of aqueous alkaline halide solutions, arefixed in troughs by means of alloys having low melting points, ratherthan being sealed in a layer of lead in accordance with the prior art.The current feed bars are arranged in longitudinal alignment and inelectrical contact with the troughs. One trough or a plurality oftroughs is assembled with each current feed bar and the troughs of eachof these assemblies are enclosed in a mass of lead or polyester resin.Each of these assemblies is accommodated in a respective recess providedin a wall of the cell. The spaces between the assemblies may be filledwith cement or a synthetic resin or asbestos cords to lend structuralintegrity to the entire anode assembly of the cell. This constructionmay finally be covered with conventional protective layers of cement andasphalt or a polyester resin resistant to attack by moist halogen andalkaline halide brine, or with a single protective layer of such apolyester resin.

This invention relates to a new construction for sealing or fixingelectrodes in an electrolytic cell and for distributing current to theelectrodes.

The construction of the present invention may be employed with respectto the fixing of electrodes in any wall of any cell. The invention,however, is particularly adapted for the fixing of anodes in the base orbottom wall of a diaphragm cell for the electrolysis of aqueoussolutions of alkaline halides. This type of cell is well known and isgenerally used for the electrolysis of alkaline chlorides to producechlorine and alkali, particularly the electrolysis of aqueous sodiumchloride solutions to produce chlorine and sodium hydroxide. In theconventional cells of this type, the plateshaped anodes are fixedvertically in the base of the cell by means of a layer of lead in whichthe current feed bars, the length of which extend perpendicular to thefaces of the anodes, are embedded. The lead serves both to hold theanodes in position and to conduct current from the feed bars to theanodes. The layer of lead is covered with a layer of cement and a layerof asphalt.

This construction for distributing current to the anodes and for fixingthe anodes in the base of the cell has a number of serious shortcomings.Major shortcomings are the following:

(1) At the temperature of electrolysis, the asphalt layer softens, whichcan result in its displacement.

(2) Halogenic organic compounds which contaminate the cell can be formedby reaction of the asphalt with the halogen formed at the anodes.

(3) The replacement of any anode or row of anodes which may deterioratein the course of electrolysis requires not only the completedisintegration of the protecting layers but also the fusion of theentire mass of lead enclosing the feed bars and the lower portions ofthe anodes. Due to the high cost of such replacement, it is noteconomically practical to do this until the end of the life cycle of thecell.

(4) The lead cast into the base of the cell contracts uponsolidification. Because this mass of lead is very substantial, thiscontraction is correspondingly substantial and, accordingly, contactbetween the lead and the anodes is quite imperfect. Accordingly, thereis substantial electrical resistance between the lead and the anodeswhereby between the lead and the anodes there is a substantial currentdrop. Furthermore, since the amount of lead employed is so substantial,the substitution for the lead of an alloy which expands upon cooling,for example, a lead-bismuth alloy, would be prohibitively costly.

(5) An oxide film tends to form at the interface of the lead and theanodes and at the interface of the lead and the current feeders. Thisfilm increases the electrical resistance between the lead and the anodesand between the lead and the current feeders thus causing a substantialdrop in current.

By the practice of the present invention, the foregoing problems areobviated. The present invention is particularly adapted for thearranging of anodes and current feeders on the base (bottom wall) or thecover (top wall) of a diaphragm cell for the electrolysis of aqueoussolutions of sodium chloride.

According to the invention, the anodes are positioned in one or moreelongated channel-shaped members, generally having a U or similarcross-section; these members may most conveniently be described aselongated troughs. With each one or more of the troughs a current feederbar is placed in electrical contact. Preferably, the current feeder baris attached to the troughs such as by brazing or welding. The currentfeeder bars are arranged in longitudinal alignment with the troughs(i.e., the lengthwise dimension of the bars is parallel to thelengthwise dimension of the troughs). The anodes are generally plates.In each of the troughs the plates are arranged in a row with one of theends of each inside the trough. Inside each trough there is provided analloy having a melting point preferably under 250 C. and occupying thespace in the trough not occupied by the plates, the alloy thereby fixingand sealing the plates in the trough. Each trough or set of troughsattached to a feeder bar, which together with the anodes mounted in thetrough or troughs comprises an anode assembly, is enclosed in a mass oflead or synthetic resin. The term enclosed" is not intended necessarilyto denote entirely enclosed since the upper edges of the troughsgenerally are exposed until the protective layer or layers are provided.

The wall of the cell in which one or more of the anode assemblies are tobe mounted is provided with a corresponding one or more recesses shapedto accommodate the final anode assemblies, i.e., the anode assembliesthe troughs of which are enclosed in the above mentioned masses. All ofthe anode assemblies are thus arranged mutually parallel in the wall ofthe cell. For convenience of installation, the masses are generally madeof such size that when the anode assemblies are installed in the cellwall the masses are laterally spaced from one another. In such case, itis preferred to fill the spaces between the masses with cement orpolyester resin or asbestos cords in order to lend greater structuralintegrity to the construction. Asbestos cords act as a resilient jointwhich allows expansion of the anode assemblies. Finally, over the entireexposed surfaces of the construction, but for the outwardly extendingunembedded portions of the anode plates, there may be providedconventional protective layers of cement and asphalt or, preferably, inplace of both layers or the latter, a protective layer of a polyesterresin.

When the cell is a diaphragm cell for the electrolysis of aqueoussolutions of alkaline halide, particularly sodium chloride, the anodesgenerally are of graphite, preferably with the ends thereof which are incontact with the 3 sealing alloy plated with copper and with tin toassure the best adhesion between the anodes and the sealing alloy.However, of course, other anodes may be used, such as of platinum-platedtitanium. The current feeders are made of a good electrical conductor,such as copper and the like. The troughs are also made of a goodconductor, such as copper, aluminum, iron and the like. A purpose of thetrough is to limit the amount of sealing alloy required and to restrictthe distances which the alloy must bridge; accordingly, the alloy may beone which contracts upon solidification, such as conventional alloys oflead and tin. Because of the small quantity of alloys involved and thesmall bridging distances, the contraction is not sufiicient tosignificantly decrease the contact between the alloy and the trough andthe alloy and anodes whereby there is no significant increase inresistance and, correspondingly, no significant current drop.Furthermore, the small quantity of alloy involved makes economicallypractical the use of alloys which expand upon solidification, whichalloys are relatively expensive. The employment of alloys which expandupon solidification assures maximum contact between the trough and thealloy and between the alloy and the anodes. Expanding alloys are wellknown and an exemplary expanding alloy suitable for use in the presentinvention is that described in Belgian Pat. No. 647,406 constituted of44.5% lead and 55.5% bismuth, by weight, and having a melting point of124 C. Examples of other alloys suitable for use in the presentinvention are the following alloys which contract upon solidification,50% Pb-50% Sn, melting point 225 C., and 33% Pb-67% Sn, melting point180 C., and the following alloy which does not undergo any perceptiblevolume change upon solidification, 60% Pb40% Bi, melting pointapproximately 180 C., all proportions being by weight. As the syntheticresin substitute for the lead, as the polyester resin between the anodeassemblies and as the polyester resin protective layer there may beemployed, for example, a bisphenol resin in styrene solution, known asAtlac A38205. Of course, on the other hand, these resins may bedifferent from one another.

The construction of the present invention greatly reduces the cost ofreplacing a single anode, plurality of anodes, an entire row of anodesor all of the anodes of the cell. Specifically, it is necessary only tomelt the alloy portions holding the anodes in question in place. Thiscontrasts sharply with the prior art, in which it was necessary in allinstances to melt a large quantity of lead covering the entire wall ofthe cell on which the anodes were mounted.

The sealing alloy is selected to have a melting point between 110 C. andpreferably under 250 C. Thus, the temperatures to which the alloys needbe heated to expeditiously melt them to remove anodes are much lowerthan the temperature of about 450 C. conventionally employed to meltlead expeditiously to remove anodes therefrom. It is preferred to heatthe alloy to a temperature of about 20 C. above its melting point forthe removal of anodes. In the construction of the present invention, thealloy or the portion of the alloy which is to be melted may preferablybe melted by means of the Joule effect. This melting may be conducted,for example, by electrically connecting one pole of the electromotiveforce source to the feeder bar and the other pole directly to the anodeto be replaced or, after removing the protective layer or layers, to thealloy itself through a highly electrically conductive sounding rod.

Another advantage of the present invention is that it is not necessaryto use any lead at all, provided that the troughs are attached to thefeeder bar, preferably by brazing, so that current may flow directlyfrom the feeder bar to the troughs. Thus, as pointed out above, a resinmay be substituted for the lead. The reason that this substiution may bemade is that, unlike in the prior art, the use of lead in thisembodiment is not necessary for the conducting of electricity. It ispreferred that the resin have a relatively high softening point, inparticular a softening point above the temperature to which the alloy isto be heated for replacement of anodes. Accordingly, when, instead oflead, a resin is used, the sealing alloy must be selected to have amelting point under 250 C. When lead is used, the alloy may have amelting point as high as 300 C.

In accordance with conventional construction, between the faces of theanodes are interposed cathodes. Since each feeder bar is in longitudinalalignment with the troughs to which it is connected and, therefore, thelengthwise dimensions of the feeder bars are parallel to the faces ofthe anodes, any shifting of the anodes caused by successive elongatingand contracting of the bars as they are heated by the flow of currentduring operation of the cell and allowed to cool during non-operation ofthe cell, has no elfect on the spacing between the anodes and thecathodes. This is another advantage of the present invention.

The invention will now be further described by reference to thedrawings, in which:

FIG. 1 is a plan view of a group of anode assemblies according to thepresent invention-mounted in a cell;

FIG. 2 is a plan view of a single one of the anode assemblies of FIG. 1;

FIG. 3 is a vertical section of the anode assembly of FIG. 2. takenthrough section line 3-3;

FIG. 4 is a vertical section of the anode assembly of FIG. 2 takenthrough section line 44;

FIG. 5 is a partial transverse section of a cell showing some of theanode assemblies of FIG. 1 mounted in the base (bottom wall) of thecell.

Individual anode assemblies (FIGS. 2, 3 and 4) are constructed outsidethe cell. A copper current feeder bar 1 is attached to the outside ofthe bottoms of two copper troughs 2 by means of brazing. A temporarymold (not shown) is constructed about this preliminary assembly topermit subsequent casting operations. A mass of lead 5 is providedaround the troughs by means of casting. In each of the troughs 2 aplurality of anodes 3 is positioned upright with their bottom endsresting on the inside of the bottom of the trough. An alloy having amelting point below 250 C. is cast into the troughs and, upon cooling,the resulting solidified alloy 4 in the troughs fixes and seals theanodes 3 in the troughs.

A plurality of the foregoing assemblies (FIGS. 1 and 5) constitutes theanodic portion of an electrolytic cell for the electrolysis of aqueoussolutions of sodium chloride. The shell of the cell is of concrete andthe bottom wall (base) 6 thereof is provided with recesses shaped toaccommodate the assemblies. The cell casing and the individualassemblies are dimensioned so that when the assemblies are installed inthe base of the cell there are lateral spaces between the assemblies.Cement or a polyester resin 7 is cast into the lateral spaces and, uponsolidification, lends rigidity and structural integrity to theconstruction. Finally, over the construction there is provided bycasting a protective layer or layers 8, which, in accordance withconventional construction, may be a layer of cement in combination witha layer of asphalt or a layer of any conventional polyester resin whichis resistant to moist chlorine and to hot sodium chloride brine or maybe a single protective layer of such a polyester resin.

While the invention has been described by reference to a particularembodiment thereof, it is to be understood that this embodiment isdescribed merely as an example and it is intended that all variationswithin the spirit of the invention be included within the scope of theappended claims.

What I claim and desire to secure by Letters Patent is:

1. An anode assembly for the electrolysis of alkali metal halidesolutions, comprising, highly electrically conductive current feederbars, a plurality of vertical graphite plates arranged in spacedparallel rows and mechanically and conductively affixed to respectivefeeder bars, said graphite plates having metal covered bases, an alloymechanically and electrically connecting the graphite plates to saidfeeder bars, said alloy melting under 250 C., said anode assemblycomprising a plurality of separate anode units electrically independent,laterally spaced and arranged mutually parallel in the bottom of anelectrolytic cell, each unit comprising one of said feed bars, at leastone highly electrically conductive channel bar mechanically andcondnctively aflixed thereto, arranged parallel to the length thereofand adapted to closely include said metal coated bases of said graphiteplates, said low-temperature melting alloy defining a solder-type bondbetween said plates and said channel bars.

2. An anode assembly according to claim 1, in which said feeder bar andsaid channel at least one bar of each anode unit are enclosed in a massof easily softened synthetic resin, having a high softening point,forming a compact aggregate.

3. An anode assembly according to claim 2, in which said bottom hasrecesses and each aggregate is accommodated in a recess in the bottom ofthe electrolytic cell.

References Cited UNITED STATES PATENTS 2,370,087 2/1945 Stuart 204-2662,987,463 6/1961 Baker et al. 204-266 3,342,717 9/1967 Leduc 204-266 XR3,390,072 6/1968 Wiseman 204-266 3,410,784 11/1968 Maunsell et al.204-290 XR 3,425,929 2/1969 Emery et al. 204-266 ROBERT K. MIHALEK,Primary Examiner D. R. VALENTINE, Assistant Examiner US. Cl. X.R.204-289, 294

